Inbreeding in Captive Reptile Populations

DISCLAIMER: Some of the images depicted in this article are provoking great discussion and argument, for the fact that none of them have been PROVEN to be directly caused by inbreeding. This is true, they have not been proven. However even with seemingly unrelated individuals breeding to produce these defective young, they still appear far more commonly in morph lines of animals than are represented in other more outcrossed and healthy genetic stock of other species that remain truer to their wild, unaltered form, unspoilt by human selective breeding. It also strikes me as odd that there could be so many incubation issues leading to serious deformities in animals that are bred in huge numbers; one would think the breeders would have the art of incubation down to a fine art. Food for thought. Of course it is easier to blame incubation issues instead of actually thinking that maybe breeding such closed genetic stock might have detrimental effects over time. In any case, the pictures are included as an illustration of what CAN happen due to close line breeding of various morphs, as well as deliberate or accidental inbreeding over time. Special thanks to Thomas Burton for allowing me to use his images, and I also wanted to mention that he has shared his own findings with breeding certain mutations in royal pythons to prevent people repeating breeding mistakes that may lead to animal suffering, which is highly commendable. More information on his findings can be found here: http://www.reptilescanada.com/showthread.php/58631-Super-Cinnamons-The-Reason-Why-Not?highlight

Captive breeding of reptiles and amphibians is a widespread activity amongst the herpetoculture hobby. It is often attempted when new owners become more proficient at caring for their reptile pets and seek to broaden their knowledge and experience with these animals thus learning about their reproductive biology. More experienced hobbyists often breed their animals as a commercial venture or indeed as a conservation effort to minimise animals being taken from the wild for the pet trade or to maintain viable captive populations of threatened species. Some commercial enterprises and indeed private keepers undertake breeding projects in order to produce large numbers of desirable species, as well as new and desirable morphs of certain species that can command high prices and therefore return an impressive profit. Captive breeding of the reptiles and amphibians one keeps is often seen as a natural progression in the hobby from having a few pets to becoming a fully-fledged ‘keeper’. As with any animal production enterprise it is important to consider the outcomes and responsibilities involved in breeding of our charges, ensuring we do so in a way that minimises suffering and maintains high standards of welfare for both the animals we breed from and ultimately any offspring we produce for the remainder of their lives.

When it comes to captive breeding of reptiles in particular, there are many concerns evident within the hobby regarding irresponsible breeding and just as many misconceptions about how the practice should be carried out in the first place. One specific concern is the issue of inbreeding in captive reptiles and the detrimental effects this is having on captive populations as a whole, animal welfare at an individual level, the ethics of captive breeding and in the current climate of animal rights opposition, the public perceptions of the hobby in general. In the following discussion I will try to address the main concerns relating to inbreeding in captive reptile and amphibian populations. This discussion assumes a basic knowledge of genetics and gene function.

So what is inbreeding and why is it important?Inbreeding can be defined as the mating of closely related individuals or those having very similar genetic constitutions. The consequences of inbreeding over time are that the offspring produced become more and more uniform in genetic similarity, and therefore the fitness of these offspring is often adversely affected. Fitness in biological terms relates to the ability of an animal to survive and reproduce thus spreading its genetic material to the next generation. This means that in the wild state those individuals that are genetically inferior and incur a disadvantage in terms of successful foraging, predator avoidance or mate acquisition for example are less likely to live and breed so ultimately their genetic contribution to the population as a whole is minimised. Survival of the fittest ensures that the wild population of any given species is maximally suited and in tune with its environment. This fitness advantage is generally achieved through the maintenance of genetic diversity, rather than uniformity, throughout the population. Genetic diversity is the biological principle that allows adaptation and evolution at a very basic level. Natural selection has ensured that any new genetic adaptations that arise through random combinations of genetic material (genes) at each mating can contribute to those genes perpetuation through the population if they are beneficial to fitness, or indeed to the elimination of such mutations if they are detrimental to fitness of the individual expressing them.

But surely inbreeding happens in the wild?Inbreeding in the wild state does indeed happen from time to time through chance for the most part, as nature has developed many strategies and biological behaviours designed to minimise the occurrence of closely related individuals breeding together. In certain species for example the ranging behaviours of male and female offspring differs greatly meaning that by the time these individuals reach sexual maturity they have a very small chance of selecting one of their offspring or even distant relatives as a mate. Similarly there is significant evidence at least in birds and mammals that individuals recognise closely related individuals and that this affects mate choice. There has not been as much evidence of kin recognition in ‘lower’ vertebrates such as reptiles and amphibians but this is an area that warrants further study. Even if inbreeding happens occasionally, on a population level of hundreds or even thousands of individuals in a geographical range the impact of this chance occurrence on fitness is minimal. Natural selection means that if any disadvantageous traits result from such a mating pattern these are unlikely to be perpetuated through the population as a whole. So while technically inbreeding can and does occur in the wild state from time to time, the implications of these few matings are minimal. This is because the healthy and advantageous genetic diversity of the population that allows it to adapt to its environment is maintained by natural behaviours of the population as a whole.

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